No, the wheel has an extendable crank handle and is meant for manual use precisely when the electronic stabilizer trim is cutout.
But aerodynamic forces can conspire to make it very hard or physically impossible for human force to rotate it if the elevator is being used to combat the stabilizer at high speeds. See here for more discussion of the physics behind it: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...
Thanks, that makes sense. When the report says that the pilots found manual trim impossible after STAB TRIM CUTOUT, do you think it's referring to an attempt at manual electric trim (expected to fail) or both pilots manually moving the trim wheels with the handle?
My (non-expert) reading is that the co-pilot couldn't move the wheel, while the pilot was engaged in fighting to to keep the stick pulled back (a Swedish pilot tried this scenario in a simulator last week and literally had to keep both arms locked around the stick towards the end).
Counter-intuitively, letting go of the stick in brief increments might have been the correct move. Letting the nose pitch down would take force off the jackscrew and let both pilots crank hard on the stabilizer. Boeing manuals once covered this, but apparently they haven't since the 1980s, and their directive after the Lion Air accident made no mention of the necessity of such a procedure. Also they were only 7,000 feet above the ground so whether or not they'd have recovered in time is hard to say. Quite possibly the MCAS had already doomed the flight.
No, it's worse: the origin airport is at 7000ft elevation. They only had around 1000ft height AGL for all of the flight. So I agree that releasing the elevator at all seems surely suicidal.
Oh! I think this is new information in the report -- the FlightRadar24 ADS-B data never shows them above 8500ft altitude, ~1000ft AGL. FlightRadar24 must have missed the final few minutes?
But high enough to re-enable a system you know is malfunctioning?
I guess we will have to wait for the final report but the pilot's actions are perplexing here. Even if we accept that they can't trim with the wheel, why enable electric trim and then not use it? Why not enable it, trim to where you want, and then use the cut out switch again?
It cuts out any electronic input, namely autopilot influence and the electric trim control present on the yoke. The trim wheel is not electric, and is the intended control when electric stabilizer control is either unavailable or intentionally disabled.
But aerodynamic forces can conspire to make it very hard or physically impossible for human force to rotate it if the elevator is being used to combat the stabilizer at high speeds. See here for more discussion of the physics behind it: https://www.satcom.guru/2019/04/stabilizer-trim-loads-and-ra...